app inventor无法构建请求数据 - 元素％不包含两个元素

I'm trying to insert in a MySql DB (via php) some data from a App Inventor 2 made form.

While testing the insert, I get in App Inventor the error 1113: unable to build request data element 1 does not contain two elements

Since I'm new to this community, I can't post images, but here's the sequence of app inventor commands involved:

• call Web1.PostText text --> call Web1.BuildRequestData list --> make a list --> make a list --> data to be inserted (all the data are copuled with their own tag in a sequence: tag1 - item 1 - tag 2 - item 2...).

It would be much simpler just to upload the image, I know...

Anyone who can help?

Thanks